Dioxane complexes of lower alkanols and magnesium halides



United States Patent Ofiice 3,466,299 Patented Sept. 9, 1969 3,466,299DIOXANE COMPLEXES OF LOWER ALKANOLS AND MAGNESIUM HALIDES Ulrich W.Weissenberg, Midland, Mich., assignor to The Dow Chemical Company,Midland, Mich., a corporation of Delaware N Drawing. Originalapplication Oct. 31, 1966, Ser. No. "590,521. Divided and thisapplication Aug. 14, 1968,

Ser. No. 770,880

Int. Cl. C07d 17/00; C07f 3/02 US. Cl. 260-340.6 4 Claims ABSTRACT OFTHE DISCLOSURE This application is a division of Ser. No. 590,521, filedOct. 31, 1966.

Numerous attempts have been made to produce anhydrous magnesium halideswhich contain less than 1 percent water and only small amounts ofoxides, but no feasible process attempted heretofore has been verysuccessful.

Chlorides, bromides and iodides of magnesium obtained by crystallizationfrom water solution are invariably hydrates. On heating these hydrates,there can be a complete or partial reversion, so that considerableamounts of magnesium oxide and/or magnesium oxyhalide are formed. Thisreversion can be suppressed to a considerable degree by heating thehydrates in an atmosphere of dry HCl, which is expensive and requirescorrosion resistant apparatus for proper functioning.

The magnesium halide hydrates can be converted to ammonium carnallitewhich then can be heated in a two stage pyrolysic to temperatures of 350C. or higher to sublime the ammonium halide. This process suflFers fromthe disadvantage that the magnesium halide must first be converted tothe carnallite, and from the fact that the sublimation is a slowreaction.

Alcoholates of magnesium halides can be obtained directly from naturallyoccuring alkali metal carnallites, particularly potassium carnallite, byleaching the latter mineral with a liquid anhydrous alcohol. On heatingthe magnesium halide-alcohol complex, however, severe decomposition ofboth the organic compound and the magnesium halide occurs, so that theend product contains relatively large amounts of carbon and magnesiumoxide.

I have found that by adding a cycloaliphatic ether to a liquidmonohydric alkanol solution of a magnesium chloride, bromide or iodide,a complex containing both the alcohol and ether is formed with themagnesium halide at room temperature. The complex is insoluble in thealcohol and in the ether in the proportions of those solvents employedand can be readily removed from the supernatant liquid by decantation,filtration or centrifuging. On heating the magnesiumhalide-alcohol-cycloaliphatic ether complex, it was surprisingly foundthat the alcohol appears to desolvate more easily than thecycloaliphatic ether. On further desolvation, the cycloaliphatic etheris volatilized Without appreciable reversion of the magnesium halide.The desolvation of the alcohol depends largely on the alcohol used.With. ethanol, this effect can be noticed at a temperature as low as 25C., particularly under vacuum. The ether is desolvated at an elevatedtemperature, usually ZOO-300 0, preferably under vacuum.

The alcohols which can be used for dissolving the magnesium halide aremonohydric alkanols which are liquid at room temperature. They can havefrom 1 to 3 carbon atoms in the alkyl group. The alcohol can be primaryor secondary, so long as it does not split: out water at temperatures upto about 150 C. The preferred alkanols are methanol and ethanol andmixtures thereof.

The cycloaliphatic ethers can be tetrahydrofurane, dioxane and loweralkyl derivatives thereof. The term lower alkyl is intended to mean agroup of from 1 to about 4 carbon atoms. These ethers have from 5 to 6atoms in the cyclic ring and 1 to 2 oxygen atoms in the ring. The onlylimitation on the type of alkyl substitution and the number of alkylgroups on the ring is that it should be so great as to increase theboiling point of the ether above about C., and that it does notdecompose with the formation of water or alcohols at its boiling point.The dioxanes can be 1,3- or 1,4-.

The magnesium halides which can be reacted and purified includemagnesium iodide, magnesium bromide and magnesium chloride. Thepreferred magnesium halide is magnesium chloride, because of itsabundance, industrial importance and potentially low cost. The magnesiumhalide can be an alcoholate dissolved in alcohol or a solution of thesalt in a monohydric alkanol of the type described.

In the preparation of the solution of the magnesium halide and in allsubsequent treatments, it is essential to maintain all ingredients asfar from water or water vapor as is practical. Thus, the alcohol usedfor preparing the solution of the magnesium halide and the cycloaliphatic ether should be of at least commercial anhydrous grade. Therecovery step for separating the magnesium halide-alcohol-cyclic ethercomplex should be carried out with a minimum exposure to moistatmospheres, and the final desolvating of the cycloaliphatic ethershould also be effected in a substantially moisture-free atmosphere andpreferably under vacuum at ZOO-300 C.

The ratio of alcohol to cycloaliphatic ether is not critical, but it isdesirable to have sufiicient ether present to form complexes of themagnesium halides having at least one mol of alcohol per mol ofmagnesium salt. Preferably, the molar ratio of alcohol to the cyclicether is from about 1 to 1 to about 20 to 1. Such complexes are not verysoluble in the alcohol-ether mixture, and thus, will precipitate fromthe liquid.

The complexes which form contain at least 0.2 mol of ether per mol ofmagnesium salt, and for this reason, the molar ratio of Mg. salt tocyclic ether should be at least 0.2 to 1 and preferably about 1 to l to2 to 1.

Representative alcohols which can. be used for dissolving the magnesiumhalide include methanol, ethanol, n-propanol and isopropanol.

Typical cyclic ethers which can be used for the formation of complexesare dioxane, tetrahydrofuran, and their alkyl or phenyl substitutedderivatives. The preferred ether is dioxane.

The examples which follow are intended to illustrate, but not to limit,the invention. Parts are by weight, unless otherwise specificallyindicated.

EXAMPLE 1 A saturated solution of MgCl in absolute methanol, obtainableby extracting potassium carnallite with anhydrous methanol, consistingof about 15 g. MgCl and about 123 g. methanol, was added rapidly withvigorous stirring at room temperature to 345 g. of absolute 1,4-dioxane.A white precipitate settled out immediately. After permitting the solidsto settle for several hours, the precipitate was filtered with theexclusion of atmospheric moisture and then subjected at a vacuum of 200mm. Hg for hours. The residue weighed 37.9 grams. On analysis, it wasshown to have the composition MgCl -1 dioxane-3 methanol.

4 EXAMPLE 3 In a series of runs, various proportions ofmagnesiumchloride were dissolved in methanol. The amount of dioxaneadded to precipitate the biligand of the magnesium salt in relation tothe amount of methanol present was also varied. In Table I below, thepercentage of magnesium is based On the Mg content of MgCl TABLEI.METHANOL, DIOXANE SOLVATES OF MAGNESIUM CHLORIDE MOLAR COMPONENTRATIOS OF PREPARED SAMPLES EXAMPLE 2 To an MgCl solution, obtainable byextracting potassium carnallite with absolute ethanol, and containing 3g. MgCl in 74 g. of the ethanol, were added 145 g. of absolute1,4-dioxane at room temperature. Crystals began to form after about 2hours. The mixture was allowed to stand overnight and then filteredwhile excluding atmospheric moisture. The crystals were washed severaltimes with absolute dioxane and held at 200 mm. Hg pressure for tenminutes. Analytical data showed that a composi- When these complexeswere subjected to heat treatment, the methanol in the complex waspreferentially released and continued heating to 290-300 C. liberatedall of the solvent to produce a magnesium chloride with a relatively lowmagnesium oxide contaminant.

Similar tests were run with ethanol. In this instance, however, theamount of magnesium chloride is recorded as percent by weight of salt.Data obtained with the ethanol containing complexes are listed in TableII.

In run 1, the analyses were made on a precipitate which was subjected toa vacuum of 100 microns of mercury at room temperature for ten minutes.The sample in run 2 was analyzed after a heat treatment of minutes at8090 C. under vacuum of microns of mercury. These data clearly show thatthe ethanol in the biligand is rapidly removed from the complex underrelatively mild conditions. Continued heating of the biligand eventuallyresults in the formation of the dioxanate of the magnesium chloride,which in turn is completely desolvated at temperatures of from about200-300 C. preferentially under vacuum in 10 to 20 minutes.

TABLE II.-ETHANOL, DIOXANE SOLVATES OF MAGNESIUM CHLORIDE:

APPROX. MOLAR RATIOS OF PREPARED SAMPLES Wt. Wt. Wt. Molar ratio, Molarratio, percent, percent, percent, dioxane- MgClr MgClz 1,4-d1oxaneethanol E+OH dioxane-E+OH Sample Run:

1 27.5 46 26 .5 Ca 1.00-1.10 Ca 1.00-1.81-2 00 2 45 40 2.0 Ca 1 .000.16Ca 1.00-1.24-0 19 I claim:

tion of MgCl -l-8 ethanol-2 dioxane can be recovered. On heating thebiligandic MgCl compound in a vacuum to 80-90 C., MgCl -2 dioxanate isobtained. Additional heating of the dioxanate under a vacuum of 50-100mm. Hg at 290300 C. yields MgCl with less than 0.5 percent MgO as animpurity.

The MgCl -6 C H OH compound when heated under substantially the sameconditions produces about as much MgO and carbon contaminants as thatformed from the corresponding methanol complex.

The dioxanate of n-propyl and isopropyl alcohol solutions of MgCl may beused for preparing biligandic complexes containing either the propanolor isopropanol and dioxane. As is the case with the ethanol and methanolcomplexes, the three carbon alcohols are preferentially removed from thecomplex, so that the dioxanate can be prepared and this then can bedesolvated to form MgCl with only small amounts of MgO contaminants andat most small traces of carbon.

Similar results are obtained with tetrahydrofuran and the other cyclicethers mentioned above.

MgI and MgBr solutions in absolute alkanols of from 1 to 3 carbon atomscan be used for preparing biligands which can be converted to dioxanatesand further desolvated to pure magnesium halides.

1. A biligand of a magnesium halide in which the halide has an atomicweight of 35 and above and said biligand consists of l to 3 mols of analkanol of from 1 to 3 carbon atoms and 1 to 2 mols of a cycloaliphaticether selected from the group consisting of 1,4-dioxane, 1,3-dioxane andtetrahydro-furan.

2. A biligand of claim 1 having the composition MgCl -3CH OH-1 dioxane.

3. A biligand of claim 1 having the composition of MgCl -2CH OH-2dioxane.

4. The composition of claim 1 in which the cyclic ether is dioxane.

References Cited Esafor, Zhur. Obshchei Khim, vol. 28, 1958, pp.1212-21.

ALEX MAZEL, Primary Examiner I. H. TURNIPSEED, Assistant Examiner US.Cl. X.R.

